France's rail network was paralysed Friday by coordinated acts of sabotage which knocked out most of its high-speed train services hours before the Paris Olympics opening ceremony.

French rail operator SNCF said three night-time arson attacks had destroyed cabling boxes at strategic junctions around its network at locations north, south-west and east of Paris.

A fourth attempted act of vandalism south-east of the capital was thwarted by rail workers who spotted intruders in the early hours of Friday.

"Our intelligence services and law enforcement are mobilised to find and punish the perpetrators of these criminal acts," Prime Minister Gabriel Attal posted on X, calling the attacks "prepared and coordinated acts of sabotage."

The Paris Olympics are set to open in a spectacular and unprecedented ceremony on the river Seine on Friday evening, with many ticket holders set to travel to the City of Light by train.

Several Eurostar trains between Paris and London were cancelled Friday because of the rail disruption, which is likely to affect British sports fans heading to the French capital.

The parade will see up to 7,500 competitors sail down a six-kilometre (four-mile) stretch of the Seine on a flotilla of 85 boats.

As well as the rail attacks, poor weather -- with Paris under thick cloud and occasional rain -- also risked dampening the party.

"We'll see tonight... but the closer it gets the more the models suggest we're likely to get rain," chief Games organiser Tony Estanguet told France Inter radio, while adding that there would be some modifications if it was wet.

"It's going to be a beautiful moment, it's going to be a great party," he added.

Hunt for culprits

French security forces are on their highest alert to prevent terror attacks spoiling the start of the first Olympics in Paris in 100 years, while acts of sabotage from hostile foreign powers were also a known risk.

French officials refused to comment on the identity of the culprits of the rail sabotage who appear to have had a sophisticated understanding of the network.

Far-left French anarchists have a history of targeting the train network with arson attacks.

Suspicions might also fall on Russia, which French President Emmanuel Macron has said in the past was planning to target the Games.

Police arrested a Russian man this week in Paris who was suspected of "organising events likely to lead to destabilisation during the Olympic Games."

Commenting on the rail disruption, which will affect 800,000 people over the weekend, International Olympic Committee president Thomas Bach told the media that he had no concerns.

"We have full confidence in the French authorities," he said at the Athletes' Village.

The USA basketball team was also set to take a high-speed train to play their opening a game on Sunday against Serbia in Lille, northern France.

Security blanket

Compared to the Covid-blighted 2020 Tokyo Olympics, which were delayed by a year and opened in an empty stadium, the Paris opening ceremony will take place in front of 300,000 ticketed spectators and many more from overlooking buildings.

It will be the first time a Summer Olympics has opened outside the main athletics stadium, a decision fraught with danger at a time when France is on its highest alert for terrorism.

A huge security perimeter has been erected along both banks of the Seine, guarded around the clock by some of the 45,000 police and paramilitary officers who will be on duty on Friday evening.

Another 10,000 soldiers are set to add to the security blanket along with 22,000 private security guards.

"Without any doubt, it is much more difficult to secure half of Paris than to secure a stadium, where you have 80,000 people and you can frisk them and send them through turnstiles," Frederic Pechenard, an ex-director general of the French police, told AFP.

Police snipers are set to be positioned on high points along the river, which is overlooked by hundreds of buildings.

President Emmanuel Macron told a pre-Games dinner for dignitaries: "Tomorrow you will have one of the most incredible opening ceremonies."

The line-up of performers is a closely guarded secret but US pop star Lady Gaga and French-Malian singer Aya Nakamura are rumoured to be among them.

US rappers Snoop Dogg and Pharrell Williams have also been in Paris for the torch relay.

Around 3,000 dancers are set to perform from the banks of the river and monuments including Notre-Dame cathedral in a show that will promote diversity, gender equality and French history.

The landmarks and architecture of the City of Light is set to feature as a backdrop both to Friday night's show and much of the sport afterwards.

Paris's vision is for a more cost-effective and less polluting Olympics than previous editions, with competitions set to take place at historic locations around the capital.

"It's going to be incredible," Laetitia Chaze, a 41-year-old landscape gardener, told AFP after arriving in Paris on a train early on Friday morning. "It's something that only happens once in your lifetime and I definitely didn't want to miss it."